Method and apparatus for inspecting foreign particle defects

ABSTRACT

The invention relates to a device production process for forming a circuit pattern on a substrate such as semiconductor device. To enable a stable inspection of a minute foreign particle and a pattern defect occurring in manufacture of a device at a high speed and with a high sensitivity, an object to be inspected on which a transparent film is formed, is irradiated with a beam which is emitted from an illuminator whose illumination direction and illumination angle are selected from a plurality of choices to be optimum, so that scattered reflected light from a minute foreign particle defect on the object or the transparent film is effectively detected by eliminating a noise from the pattern formed on the object, and a detection optical system is optimized by evaluating and adjusting, with an image forming performance checker, an image forming performance of the detection optical system included in an inspecting apparatus.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for inspecting,in a process of manufacturing a semiconductor device, foreign particlesor a state of occurrence of defects, which method and apparatus isrelevant to a step of detecting, analyzing, and taking measures againsta foreign particle on a thin film substrate, semiconductor substrate,photomask, and other objects that are produced in manufacture of asemiconductor chip or a liquid crystal product, as well as a defect in acircuit pattern in the thin film substrate, semiconductor substrate,photomask and others.

In a process of producing a semiconductor device, a foreign particlepresent on a semiconductor substrate or a wafer leads to a defect suchas defective insulation of wiring and short-circuit. With a recent trendof miniaturization of semiconductor devices, a minute foreign particlecould be a cause of defective insulation of a capacitor or damage of agate oxide film or others. Such a foreign particle is produced andintroduced in various ways. For instance, the foreign particle may comefrom a movable portion in a feeding device or a human body, may begenerated as a reaction product in a processing apparatus during aprocess using a process gas, or may come from chemicals or materials.

Similarly, in a process of producing a liquid crystal display element,when a defect is caused in a pattern by the foreign particle introducedin the above-described manner, the finished display element does notwork. With a process of producing a printed circuit board or a printedwiring board, the circumstances is the same, namely, introduction of aforeign particle causes a short-circuit in a pattern or a badconnection. Hence, in manufacture of semiconductor devices, one (or morein some situations) foreign particle inspecting apparatus is disposed ineach production line so as to detect a foreign particle at an earlystage and feed back a result of the detection, in order to improve theyield rate.

One of techniques of this kind to detect a foreign particle on asemiconductor substrate is disclosed in JP-A-62-89336, which teaches toirradiate a semiconductor substrate with a laser beam and detectscattered light from a foreign particle adhering to the semiconductorsubstrate. The result of the inspection is compared with a result of aninspection last performed for the same kind of semiconductor substrate,so as to eliminate the possibility of misdetection of a pattern andenable a highly sensitive and reliable inspection of foreign particledefects. Disclosed in JP-A-63-135848, there is known another techniquein which a semiconductor substrate is irradiated with a laser beam andscattered light from a foreign particle adhering to the semiconductorsubstrate is detected, and the detected foreign particle is analyzed bya method such as laser photoluminescence spectroscopy and secondaryX-ray analysis (XMR).

As a technique to inspect foreign particles as mentioned above, there isknown a method such that a wafer is irradiated with coherent light, andlight emitted from a repetitive or periodic pattern on the wafer isremoved by a spatial filter so that a foreign particle and a defect thatare irregular or not periodic are emphasized to be detectable. Further,JP-A-1-117024 discloses a foreign particle inspecting apparatus wherelight is emitted toward a circuit pattern on a wafer in a direction45-degree inclined with respect to directions of straight segments ofprincipal groups in the circuit pattern and the zeroth-order diffractionlight from the straight segments of the principal group is preventedfrom entering an aperture of an objective lens. The publicationJP-A-1-117024 also teaches to block light emitted from straight segmentsof the other group than those of the principal groups by a spatialfilter.

A technique related to an apparatus and method for inspecting a defectsuch as presence of a foreign particle is disclosed in JP-A-1-250847 andJP-A-2000-105203. The publication JP-A-2000-105203 teaches to change apixel size at which detection is performed, by enabling switchingassociated with the detection optical system used for the detection, andto inspect a foreign particle by illuminating a substrate with lightcondensed in one direction. JP-A-2001-60607 discloses a technique tomeasure a size of a foreign particle.

However, any of the above-described conventional techniques does notsucceed to detect with ease, at a high speed, and with a highsensitivity, a minute foreign particle or defect on a substrate on whicha periodic pattern and a non-periodic pattern are present in a mixedmanner. That is, the conventional techniques can not solve a problemthat at a portion other than a periodic pattern such as memory cellportion, the detection sensitivity is low, or a minimum particle sizedetectable is large. Further, according to the conventional techniques,the detection sensitivity for a minute foreign particle or a defect onthe order of 0.1 μm in an area where the pattern density is high is low.Still further, the detection sensitivity is low for a foreign particleor a defect that causes a short-circuit between wires, and for a foreignparticle in the form of a thin film. The conventional techniquedisclosed in JP-A-2001-60607 has drawbacks that the measuring accuracyand precision for a foreign particle or a defect is low, and thedetection sensitivity for a foreign particle on a wafer coated with athin transparent film is low.

SUMMARY OF THE INVENTION

The invention has been developed in view of the above-described problemsand thus an object of the invention is to provide a defect inspectingmethod and apparatus capable of inspecting a minute foreign particle ordefect on the order of 0.1 μm on a substrate as an object of inspectionin which a periodic pattern and a non-periodic pattern are present in amixed manner, at a high speed and with a high accuracy and precision,and more particularly a method and apparatus for stably detecting adefect by using a plurality of defect inspecting apparatuses of the samestructure in a production line of semiconductor devices or others, byreducing a variation in the performance among the detecting apparatuses.

Thus, the invention provides an apparatus for inspecting a foreignparticle defect, comprising:

-   -   an illuminator which irradiates a surface of a sample with an        illuminating beam;    -   a detector which collects through an objective lens scattered        reflected light from the surface of the sample as illuminated by        the illuminator and detects the collected light with a detecting        device; and    -   a signal processor which processes a signal obtained as a result        of the detection of the scattered reflected light by the        detecting device of the detector so as to detect a defect on the        surface of the sample,    -   wherein the detector includes a converging optical system which        collects the scattered reflected light from the surface of the        sample, and an aberration corrector which corrects an aberration        of the converging optical system.

The illuminator has a first illuminating portion which irradiates thesurface of the sample with an illuminating beam from a high angle, and asecond illuminating portion which irradiates the surface of the samplewith an illuminating beam from a low angle.

The converging optical system of the detector includes a reflectionoptical system and a refraction optical system, and the aberrationcorrector corrects the aberration of the converging optical system bychanging a condition of reflection of the reflection optical system or acondition of refraction of the refraction optical system.

The converging optical system of the detector further includes an imageforming magnification changer which changes an image formingmagnification of the converging optical system while a position of theobjective lens relatively to the detecting device is fixed.

The illuminating beam emitted from the illuminator toward the surface ofthe sample is formed in a shape long in a direction, and emitted from adirection oblique to the surface of the sample.

Further, the detector is adapted such that a relative distance between asubstrate to be inspected and the detecting device is fixed and theimage forming magnification is variable. An image forming optical systemof the detector is adapted such that a size of a Fourier transform imageis fixed while the image forming magnification is variable.

The invention also provides an apparatus for inspecting a foreignparticle defect, comprising:

-   -   an illumination optical system including an illumination light        source which emits an illuminating beam toward a surface of a        substrate to be inspected, an angle of the illuminated beam        being switchable between a high angle and a low angle;    -   a detection optical system including: an objective lens which is        disposed at a position optimum for collecting scattered        reflected light from a foreign particle defect on the substrate        and collects the scattered reflected light from the foreign        particle defect; an image forming optical system which forms an        image of the scattered reflected light as collected by the        objective lens; and a light detecting device which receives the        image of the scattered reflected light formed by the image        forming optical system, and converts the image into an image        signal;    -   an A/D converting portion which converts the image signal        obtained by the light detecting device of the detection optical        system when the illumination optical system emits the        illuminating beam at the high angle or the low angle, into a        digital image signal;    -   a defect detecting and processing portion which detects a        foreign particle defect based on the digital image signal; and    -   a confirming device which enables to confirm the detected        foreign particle defect.

The defect inspecting apparatus according to the invention includes ameasurer which measures an aberration of the detection optical systemand a corrector which corrects the aberration, so as to enable a stabledetection of defect, and a comparison is made between current data onthe detection optical system and data thereon at the time ofinstallation of the detection optical system in the defect inspectingapparatus, and a correction is made based on a result of the comparison,in order to enable a stable detection of a foreign particle defect for along term, as well as reduce a performance variation among a pluralityof the defect inspecting apparatuses having the same structure. Thus, itis enabled to reduce diffracted light from the circuit pattern on thesubstrate such as LSI pattern, thereby enabling an inspection of aminute foreign particle or a defect, a minute foreign particle or adefect that short-circuits the wires, and a thin film-like foreignparticle, at high speed and with high accuracy and precision.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a defect inspecting apparatus accordingto one embodiment of the invention.

FIG. 2A is a schematic view of an illumination optical system of thedefect inspecting apparatus shown in FIG. 1, and

FIG. 2B is a perspective view illustrating how the illumination opticalsystem is constructed, and FIG. 2C is a plan view of a wafer asilluminated by the illumination optical system.

FIG. 3A shows a state where the wafer is irradiated with a laser beamfrom a direction at an angle φ with respect to a scanning direction of aY-stage, i.e., a Y-axis direction of the wafer, and at an angle α withrespect to a Z-axis direction of the wafer, to form a slit-like beam onthe wafer, and FIG. 3B shows a state where the wafer is irradiated witha laser beam from a direction that is parallel to the Y-axis directionto form the slit-like beam on the wafer, with a longitudinal directionof the slit-like beam parallel to the direction from which the laserbeam is incident.

FIG. 4A is a schematic view of a detection optical system of the defectinspecting apparatus, and FIG. 4B is a schematic view of amagnification-variable image forming optical system of the detectionoptical system.

FIG. 5A is a view of an image of reflected diffracted light from aperiodic pattern on the wafer in a field of vision of a pupilobservation optical system of the defect inspecting apparatus, FIG. 5Bshows a light blocking pattern of a spatial filter, and FIG. 5C is aview of the field of vision when the image of the reflected diffractedlight is filtered with the spatial filter.

FIG. 6 is a block diagram of an interferometer apparatus according tothe embodiment.

FIG. 7 illustrates how a rear lens group of the detection optical systemis adjusted using the interferometer apparatus.

FIG. 8A is a view of interference fringes as observed with theinterferometer apparatus and occurring when the rear lens group is notproperly adjusted, and FIG. 8B is a view of interference fringesobserved with the interferometer apparatus and occurring when the rearlens group is properly adjusted.

FIG. 9 is a flowchart illustrating a procedure of the adjustment of therear lens group illustrated in FIG. 7.

FIG. 10 is a diagram illustrating how a front lens group of thedetection optical system is adjusted using the interferometer apparatus.

FIG. 11 is a flowchart illustrating a procedure of the adjustment of thefront lens group illustrated in FIG. 10.

FIG. 12 is a diagram illustrating an overall adjustment of the detectionoptical system.

FIG. 13A is a schematic view of a reflection varying unit, FIG. 13Bshows one example of a spacer of the reflection varying unit on whichspacer a plurality of protrusions are arranged, and FIG. 13C showsanother example of the spacer on which a plurality of sectorial,concentric protrusions are arranged.

FIG. 14 shows a general structure of the defect inspecting apparatus.

FIG. 15 is a block diagram of a signal processing system shown in FIG.1.

FIG. 16 is a diagram illustrating a threshold calculating and processingportion.

FIG. 17 is a schematic diagram of the defect inspecting apparatusincluding an observation optical system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, there will be described one embodiment of the invention, byreferring to the accompanying drawings.

A defect inspecting apparatus according to the invention detects with ahigh sensitivity and at a high speed foreign particles and various kindsof defects such as pattern defect and microscratch on various kinds ofsubstrates such as wafer as an object of a defect detection in varioussteps in a production process. In particular, the defect inspectingapparatus stably detects defects on a thin film formed on a wafer bydistinguishing the defects from defects inside the thin film.

That is, the defect inspecting apparatus of the invention is adaptedsuch that an illumination angle α and an illumination direction φ of aslit-like beam 201 emitted from an illumination optical system 10, asshown in FIG. 2A, are changeable depending on an object to be inspected,a detection optical system 20 is disposed such that a relativepositional relationship between a surface of the object to be inspectedand a light receiving surface of a light detecting device 26 is set suchthat an image of the surface of the object is formed on the lightreceiving surface, and an image forming magnification of the detectionoptical system 20 is variable so that an inspection can be made at adetection pixel size suitably set depending on a size of a defect to bedetected.

Further, the defect inspecting apparatus has a function to distinguishdifferent kinds of detected defects by using, as a characteristicquantity, a difference in scattered light from defects illuminated withan illumination beam from a plurality of illumination angles, forinstance.

Initially, a defect inspecting apparatus according to one embodiment ofthe invention will be described in detail. In the embodiment below, theinvention is applied to an inspection of a minute or large foreignparticle and a microscratch on a semiconductor wafer or a transparentfilm formed thereon, a foreign particle in the transparent film, and adefect such as pattern defect. However, the object to be inspected by anapparatus or a method according to the invention is not limited to asemiconductor wafer but may be a thin film substrate, photomask, TFT, orPDP, for instance.

FIG. 1 shows a structure of a defect inspecting apparatus according tothe embodiment of the invention. This defect inspecting apparatusincludes an illumination optical system 10, a magnification-variabledetection optical system 20, a feeding system 30, a signal processingsystem 40 and a general controller 50 for an overall control of thedefect inspecting apparatus.

The feeding system 30 includes an XY-stage 31, a Z-stage 32, and aθ-stage 33, for placing on a sample table 34 a wafer 1 as an example ofa substrate to be inspected, and displacing the wafer 1. The feedingsystem 30 further includes a controller 35 for controlling theses stages31, 32, 33. The wafer 1 may be of various kinds seen in variousproduction steps.

The illumination optical system 10 includes a laser light source 11, abeam expander optical system 16, mirrors 254, 256, and a lens 255, andenlarges light as emitted from the laser light source 11 to a size bythe beam expander optical system 16, and irradiate the wafer 1 with theenlarged beam in a plurality of oblique directions via the mirrors 254,256, the lens 255, and others.

The detection optical system 20 includes an objective lens 21, areflection varying unit 100, a spatial filter 22, an image forming lens23, an optical filter 25, a light detecting device 26 such as TDI imagesensor.

In an optical path of the detection optical system 20, a wavefrontmeasuring optical system 150 is disposed. The wavefront measuringoptical system 150 includes a mirror 151 and a detecting device 152. Themirror 151 is movable between a position in the optical path of thedetection optical system 20 and another position retracted from theoptical path. A parallel light flux emitted from the wafer 1 is incidenton the objective lens 21 and detected by the detecting device 152 by wayof the mirror 151, when an image forming performance of the opticalsystem 20 is checked.

A signal processing system 40 processes an image signal detected by thelight detecting device 26 so as to detect a defect and a foreignparticle.

An observation optical system 60 includes a lens 61, a polarizing beamsplitter 62, an illumination light source 63, and an imaging device 64,and illuminates a surface of the wafer 1 by the illumination lightsource 63, so as to confirm the presence/non-presence and the shape of aforeign material as detected in advance by another inspecting apparatus.

The general controller 50 operates to set conditions of an inspectionand generally controls the illumination optical system 10, themagnification-variable detection optical system 20, the feeding system30, and the signal processing system 40. The general controller 50includes an input/output device 51 including a keyboard and a network, adisplay device 52, and a memory device 53.

The defect inspecting apparatus further includes an autofocus controlsystem (not shown) which makes an image on the wafer 1 to be formed on alight receiving surface of the light detecting device 26.

This defect inspecting apparatus is adapted such that the wafer 1 can beirradiated with an illumination beam from a plurality of directions. Asshown in FIG. 2A, the illumination optical system 10 includes the beamexpander optical system 16, a lens 14, and a mirror 15. The beamexpander optical system 16 may include a concave lens and a convex lens,for instance, and enlarges a beam L0 as emitted from the laser lightsource 11.

As shown in FIGS. 2B and 2C, the defect inspecting apparatus is capableof emitting a slit-like beam 201 toward the wafer 1 as an object to beinspected and put on a sample table 34, in a plurality of directions inplan view, namely, four directions 220, 230, 240 and 250 as shown inFIGS. 2B and 2C, and at a plurality of illumination angles.

The reason why the illumination beam 201 is slit-like is that lightscattered from a foreign particle or a defect when the wafer 1 isilluminated is detected at once by a row of light receiving elements inthe light detecting device 26, so that the speed of the foreignparticle/defect inspection is enhanced.

An orientation of the wafer 1 on the table 34 is adjusted such that theθ-stage 33 is moved so that directions of a row and a column of a matrixof chips 202 on the wafer 1 coincide with directions of movement of theXY-stage 31. The slit-like beam 201 is emitted toward the wafer 1 whoseorientation has been thus adjusted.

The slit-like beam 201 emitted toward the wafer 1 is adjusted by anoptical system which converges light in an X-axis direction (which isone of two directions in which the XY-stage 31 is movable) and directsthe light into parallel rays in a Y-axis direction (which is the otherdirection in which the XY-state 31 is movable), such that an opticalaxis of the beam 201 is perpendicular to the X-axis direction, andparallel to the Y-axis as well as a direction of alignment 203 (shown inFIG. 2C) of pixels of the light detecting device 26. Thus, alongitudinal direction of the slit-like beam 201 incident on the wafer 1is perpendicular to the X-axis direction, and parallel to the Y-axisdirection. This arrangement facilitates alignment among the chips when acomparison is made among image signals representative of the chips. Sucha slit-like beam 201 can be formed by disposing a conical lens 14 or acylindrical lens 244, for instance, in the optical path, as shown inFIGS. 3A and 3B.

To form the slit-like beam 201 on the wafer 1 when the illumination ismade from a direction 220 or 230, a laser beam is emitted from adirection at an angle φ with respect to the Y-axis direction on one oftwo opposite sides (i.e., on the left or right side in FIG. 2C), andinclined at angle α in the Z-axis direction. In FIG. 2B, a first segmentof the optical path of the illumination beam from the direction 230,which is from a mirror 233 to a mirror 235 via a cylindrical lens 234,and a second segment thereof which is from the mirror 235 to an areairradiated with the slit-like beam 201 on the wafer 1, overlap. Torealize such illumination, a lens 14 (shown in FIG. 3 and correspondingto cylindrical lenses 224, 234 in FIG. 2B) having a conical curvedsurface whose radius of curvature in a longitudinal directioncontinuously varies is disposed in the optical path, so that thelongitudinal direction of the slit-like beam 201 is parallel to theY-axis direction.

When the illumination is made from a direction 250, the wafer 1 isilluminated in a direction parallel to the Y-axis direction and thelongitudinal direction of the slit-like beam 201, and the beam 201 canbe formed in the slit-like shape by being passed through a cylindricallens 255 (having the same shape as the cylindrical lens 244 shown inFIG. 3B).

When the illumination is made from a direction 240, the wafer 1 isilluminated in a direction parallel to the Y-axis direction andperpendicular to the longitudinal direction of the slit-like beam 201,and thus the beam 201 can be formed in the slit-like shape by beingpassed through a cylindrical lens 244 disposed at an angle of 90 degreeswith respect to the cylindrical lens 255.

The illumination optical system 10 is constructed such that the mirror15 and a mirror 205 are switchable based on an instruction from thegeneral controller 50, as shown in FIG. 2A, so that the illuminationangle α is changeable depending on the kind of foreign particle on thewafer 1 to be inspected, for instance. As shown in FIG. 2C, theslit-like beam 201 has an illuminating area covering the row 203 of thepixels of the light detecting device 26, regardless of what theillumination angle is. That is, the position the slit-like beam 201 isincident on the wafer 1 is constant irrespective of from which directionthe illumination beam is incident, even where the direction of theincidence is not one of the above-mentioned directions, such as when theincident direction is a direction opposite to the direction 220 or 230.

Thus, an illumination with parallel light in the Y-axis direction and atan angle φ of about 45 degrees is achieved. By having the slit-like beam201 in the form of the parallel light in the Y-axis direction,diffracted light from a circuit pattern whose straight segments of amain group is oriented in the X-axis or Y-axis direction is blocked bythe spatial filter 22.

The conical lens 14 may be produced according to a production methoddisclosed in JP-A-2000-105203, for instance.

The present defect inspecting apparatus is constructed such that theslit-like beam 201 is formable on the wafer 1 from a plurality ofillumination angles, in order to enable detection of various kinds offoreign particles and defects on the wafer 1. That is, an object ofinspection by the apparatus is a defect of a pattern on the wafer 1 anda foreign particle whose height is small.

With an increase in the illumination angle α, an amount of the reflecteddiffracted light from the circuit pattern increases and the S/N ratiodecreases, and thus an empirically obtained optimum angle is employed.For example, when a foreign particle having a small height is to bedetected, the illumination angle α is preferably small, e.g., about 1 to10 degrees, and more preferably about 1 to 5 degrees. In another casewhere a foreign particle between wires or a pattern defect is to bedetected in a wiring step, the illumination angle α is preferably large,i.e., about 40 to 60 degrees, and more preferably 45 to 55 degrees,taking account of the S/N ratio related to the difference between thepattern and the foreign particle/defect. Where there is a fixedcorrespondence between a step in which the inspection is implemented andthe kind of foreign particle/defect desired to be detected, theillumination angle may be predefined in an inspection recipe. To detecta foreign particle/pattern defect on the wafer evenly, the illuminationangle may be set at a value between the above-mentioned values, that is,a value between 5 and 45 degrees.

When the inspection is performed in a wiring step, the illuminationdirection φ is preferably aligned with the wiring pattern formed on thewafer so as to facilitate detection of a foreign particle between wires.Where the circuit pattern on the wafer is not a wiring pattern but isconstituted by contact holes, capacitors, and/or others, there is nospecific orientation in the circuit pattern, and thus it is desirablethat the illumination beam is incident in a direction of about 45degrees with respect to a chip in question. A change in the illuminationangle is made, for instance, by switching between two mirrors 15, 205inclined at different angles, as shown in FIG. 2, or by rotating themirror 15 (or 205) around an axis extending in the X-axis directionperpendicular to a surface of the sheet in which the FIG. 2A ispresented, by means of a rotating device (not shown). The mirror 15 ismoved in the Z-axis direction also so that the slit-like beam 201 isaligned on the wafer 1 with a detection optical axis of the detectionoptical system, and the lens 14 is also adjusted or moved in the Z-axisdirection so that the slit-like beam 201 has a minimum diameter on thedetection optical axis of the detection optical system.

There will be now described how to change the illumination direction, byreferring to FIG. 2B. In FIG. 2B, reference numeral 218 denotes asplitting optical element consisting of a mirror, a prism, and others.The splitting optical element 218 is moved in the Y-axis direction by adrive means not shown, so as to allow the laser beam L0 as emitted fromthe laser light source 11 to pass through the element 218, or reflectthe laser beam L0, to direct the beam in one of three directions. Thelaser beam L1 transmitted through the splitting optical element 218 issplit into a transmitted component and a reflected component by a halfprism 221. The transmitted component is, for instance, then transmittedthrough a wave plate 236 and reflected by a mirror 231, a beam diametercorrection optical system 232, the mirror 233, the conical lens 234, andthe mirror 235, so as to form the slit-like beam 201 on the wafer 1 fromthe direction 230.

On the other hand, the reflected light from the half prism 221 alsoforms the slit-like beam 201 on the wafer 1, via optical elements havingthe same functions as mentioned above with respect to the transmittedcomponent from the half prism 221, namely, a beam diameter correctionoptical system 222, a wave plate 226, a mirror 223, a cylindrical lens224, and a mirror 225. The beam diameter correction optical systems 222and 232 adjust the beam diameter of the laser beam incident on theconical lens 14 so that the slit-like beam 201 incident on the wafer 1has a constant size. When a mirror 260 is disposed in place of the halfprism 221, illumination is possible only from the direction 220, whilewhen neither the half prism 221 nor the mirror 260 is used, illuminationis possible only from the direction 230. By disposing wave plates 226,236 in both the optical paths on the rear side of the half prism 221,the polarizing direction of the emitted laser beam can be made the same.

A laser beam L2 reflected by the splitting optical element 218 istransmitted through the beam diameter correction optical system 241,then reflected by mirrors 242 and 243, transmitted through a cylindricallens 244, and again reflected by a mirror 245, so as to form theslit-like beam 201 on the wafer 1 from the direction 240.

A laser beam L3 also forms the slit-like beam 201 on the wafer 1 fromthe direction 250, via optical elements similar to those in the opticalpath of the laser beam L2, namely, a mirror 251 which reflects the beamL3, a beam diameter correction optical system 252 which transmits thelaser beam L3, mirrors 253 and 254 that reflect the laser beam L3, thecylindrical lens 255, and a mirror 256 which reflects the laser beam L3.

For instance in a wiring step and where a wiring pattern formed on thewafer includes many segments extending in the X-axis direction or theY-axis direction, the direction 240 or 250 of illumination coincideswith the direction in which many segments of the wiring pattern extend,thereby facilitating detection of a foreign particle between wires.

In the present embodiment, a high-power YAG laser of 532 nm secondharmonic wavelength is used as the laser light source 11. However, it isnot essential that the wavelength be 532 nm, but an UV laser, a deep UVlaser, or a vacuum UV laser may be employed. Further, the light sourcemay be other lasers such as Ar laser, nitrogen laser, He—Cd laser,excimer laser, and semiconductor laser.

In general, a decrease in the wavelength of the laser improves aresolution of a detected image, thereby enabling a highly sensitiveinspection.

There will be next described the detection optical system 20 shown inFIG. 4A. The detection optical system 20 is constructed such thatreflected diffracted light from the object substrate in the form of thewafer 1 is detected by the light detecting device 26 such as TDI imagesensor, via the objective lens 21, the reflection varying unit 100, thespatial filter 22, the image forming lens (magnification-variable imageforming optical system) 23, a density filter, an optical filter group420 including a polarizing plate. When a TDI sensor is used as the lightdetecting device 26, the TDI sensor may be one having a plurality ofoutput taps to output a plurality of signals in parallel, so that thesignal processing system 40 processes the signals in parallel using aplurality of processing circuits and a plurality of processing programs,thereby enabling a detection at high speed.

The spatial filter 22 operates to block a Fourier transform image of thereflected diffracted light from a periodic pattern on the wafer 1 andallows scattered light from a defect/foreign particle to passtherethrough. The spatial filter 22 is disposed at an image formingposition (corresponding to an exit pupil) with respect to the objectivelens 21 in the spatial frequency domain, i.e., the Fouriertransformation.

Adjusted as follows, the spatial filter 22 is disposed in the opticalpath of the detection optical system 20. Initially, using a pupilobservation optical system 70 including a mirror 90 that is retracted inthe X-axis direction during an inspection, a projector lens 91, and a TVcamera 92, an image 502 of the reflected diffracted light from aperiodic pattern, at the image forming position of the Fouriertransformation in a field of view 501 of the pupil observation opticalsystem 70, is taken, as indicated by white points in FIG. 5A, forinstance. Then, intervals p of rectangular light blocking portions of ascreen 503 as shown in FIG. 5B which is disposed at the image formingposition of Fourier transformation is mechanically changed by a suitablemechanism (not shown) so that the rectangular light blocking portionsblock the image 502 of the reflected diffracted light. Thus, anadjustment is made to obtain an image 504 without a luminescent spot ofthe image of the reflected diffracted light from the pattern, as shownin FIG. 5C, at the image forming position of the Fourier transformation.These steps are implemented by the signal processing system 40processing signals from the TV camera 92 based on an instruction fromthe general controller 50. The screen 503 is not limited to theabove-described one, but may be replaced with a screen where the lightblocking portions are formed on a transparent substrate using a liquidcrystal display element, based on an image signal from the TV camera 92.That is, black portions as light blocking portions and white portionsare made by operating the liquid crystal display element to form thelight blocking portions suitable for the image taken by the TV camera92.

The defect inspecting apparatus is operable in one of a high-speed modeto implement the inspection at a high speed, and a low-speed mode toimplement the inspection at a low speed but with a high sensitivity.That is, where the circuit pattern on the object at an area to beinspected is formed in a high density, the magnification of thedetection optical system is increased to obtain an image signal of highresolution, thereby enabling an inspection at high sensitivity. On theother hand, where the circuit pattern on the object at an area to beinspected is formed in a low density, the magnification of the detectionoptical system is decreased to enable an inspection at high speed whilemaintaining the high sensitivity. Thus, the size of foreignparticle/defect to be detected and the detection pixel size areoptimized, and only scattered light from the foreign particle/defect isefficiently detected with noise from materials other than foreignparticle/defect eliminated. In this way, in the defect inspectingapparatus, the magnification of the detection optical system 20 disposedabove the wafer 1 is made variable with a simple structure.

There will be described how to change the magnification of the detectionoptical system, by referring to FIGS. 4A and 4B.

A change in the magnification of the detection optical system is madebased on an instruction from the general controller 50. The imageforming lens 23 is constituted by movable lenses 401, 402, 403 and amoving mechanism 404. When the magnification is changed, themagnification of the image of the surface of the wafer as formed on thedetecting device 26 is changeable without changing the positions of theobjective lens 21 and the spatial filter 22 in a direction of theoptical axis. That is, when the magnification is changed, a relativeposition between the object substrate (wafer) 1 and the light detectingdevice 26 needs not be changed. Thus, the moving mechanism 404 operatedto change the magnification is simple in structure, and an area size ofFourier transformation is not changed, thereby making it unnecessary toreplace the spatial filter 22.

The magnification M of the detection optical system 20 is obtained bythe following equation 1, where f₁ represents a focal length 405 of theobjective lens 21, and f₂ represents a focal length 406 of the imageforming lens 23:M=f ₂ /f ₁  (1)

Hence, to set the magnification of the magnification-variable detectionoptical system 20 at M, the movable lenses 401-403 are moved topositions that makes f₂ equal to (M×f₁), since f₁ is a constant.

There will be described in detail the moving mechanism 404 shown in FIG.4A, by referring to FIG. 4B. FIG. 4B shows a detailed structure of theimage forming lens 23 (shown in FIG. 4A) including the movable lenses401-403 and the moving mechanism 404, and illustrates how to move andposition the movable lenses 401, 402, 403 at specific positions. Themovable lens 401 is held by a lens holder 410 that is movable on alinear guide 450 in a direction of the optical axis by driving a ballscrew 412 by a motor 411. The movable lenses 402 and 403 are held bylens holders 420 and 430, respectively, and individually movable on thelinear guide 450 by driving of ball screws 422, 432 by motors 421, 431.

Movable portions 415, 425, 435 of positioning sensors are disposed atends of the respective lens holders 410, 420, 430 holding the movablelenses 401, 402, 403, while detecting portions 416-418, 426-428, 436-438of the positioning sensors are disposed at positions where the movablelenses 401, 402, 403 are to be stopped. The stop positions correspond torespective magnification levels. The motors 411, 421, 431 are driven tomove the lens holders in the direction of the optical axis and the lensholders are positioned by detecting the movable portions 415, 425, 435of the positioning sensors by the detecting portions 416, 426, 436 thatare at positions corresponding to a desired magnification. Thepositioning sensors 417, 418 are an upper limit sensor and a lower limitsensor for the movable lens 401 in the direction of the optical path,and each of the movable lenses 402, 403 also has the same limit sensors427, 428 and 437, 438. The positioning sensors may be optical ormagnetic sensors, for instance.

The moving mechanism 404 is operated based on an instruction from thegeneral controller 50. That is, the magnification is set depending oninformation on a surface the object substrate 1 on the stage and theproduction process, so that minute foreign particles/defects aredetectable as many as possible. For instance, where the circuit patternon the object substrate 1 is formed in a high density, a mode forinspection at high magnification and with high sensitivity is selected,while where the circuit pattern is formed in a low density, a mode forinspection at low magnification and high speed is selected.

In this way, the detection optical system of the defect inspectingapparatus can cover a wide range of magnification with a single lenssystem. However, the number of lenses of a lens group constituting thedetection optical system is increasing, and also there is an increasingdemand for high surface precision and high assembly precision. Inaddition, there emerges a need to deal with mechanical vibrations in thedefect inspecting apparatus and an environmental change such astemperature change.

Hence, the detection optical system of the defect apparatus according tothe invention allows the illumination beam having the same wavelength asan inspection illumination beam, to pass the detection optical system,and detects a wavefront aberration of the transmitted light, therebyenabling to monitor the image formation performance of the opticalsystem 20.

For instance, in the optical system shown in FIG. 2B, the laser beam L0emitted from the laser light source 11 and passes through the beamexpander optical system 16 is reflected by the splitting optical element218. The reflected laser beam now denoted by L3 is reflected by themirror 254, and incident on a condenser lens 308 via mirrors 306, 307,with the lens 255 and mirror 256 retracted from the optical path, so asto form, by the condenser lend 308 and on a back side of the wafer 1, aspot of light at the same position in the Z-axis direction as a place tobe inspected on an upper side of the wafer 1.

A structure of an optical system 309 for monitoring the image formationperformance of the detection optical system 20 is shown in FIG. 1 also.As shown in FIG. 2, the laser beam L0 travels from the mirror 306 towardthe mirror 307 in the Y-axis direction. In FIG. 1, however, in themonitoring optical system 309, the laser beam is represented as if thebeam travels from the mirror 306 to the mirror 307 along the X-axisdirection, for the sake of convenience.

The laser spot formed by the condenser lens 308 passes through theobjective lens 21 of the detection optical system 20 shown in FIG. 1, tobecome a parallel light flux, that is reflected by the reflectionvarying unit 100 and then by the mirror 151 disposed between thereflection varying unit 100 and the image forming lens 23 to beretractable from the optical path in the Y-axis direction, and isincident on the wavefront detecting device 152.

The reflection varying unit 100 includes a plurality of actuators 110arranged in the X-axis and Y-axis directions on a support plate 102 asshown in FIG. 13A, a spacer 106, and a reflecting mirror 105. Theactuators 110, spacer 106, and reflecting mirror 105 are fixed to thesupport plate 102 by a holder plate 103. Each actuator is, for instance,a piezoelectric element or a device directly driven by motor. Acontroller 115 converts electrical signals from a fringe analyzingapparatus 350 (shown in FIG. 6) into drive signals to drive theactuators 110.

The spacer 106 between the reflecting mirror 105 and the actuators 110is an elastically deformable member, which has, for instance, aplurality of protrusions 107 as shown in FIG. 13B, or a plurality ofprotrusions arranged concentrically and along a circumference as shownin FIG. 13C. The actuators 110 are arranged so that a pressure acts oneach of the protrusions. A reflecting surface of the reflecting mirror105 is slightly deformed by a small displacing force or pressurecorresponding to an electrical signal from the controller 115. The wayof deforming the reflecting mirror is not limited to the above-describedone, but there may be employed a mirror including a plurality ofreflecting mirrors produced by a process of producing semiconductordevices or otherwise, and with an integrally formed driving system.

For instance, the wavefront detecting device 152 is a CCD camera wherelight receiving elements are arranged in a matrix, and the parallellight flux is focused on the light receiving elements by condenserlenses arranged in a matrix near a light receiving surface. Forinstance, where a wavefront of the parallel light flux is irregularbecause of an aberration of the optical system, output signals from thelight receiving elements vary and a discontinuity occurs. The generalcontroller 50 processes the image signal outputted from the wavefrontdetecting device 152 to calculate an amount of the wavefront aberration.A comparison is made between the calculated wavefront aberration anddata on the lenses of the detection optical system 20 at the time of theproduction which data is stored in a storage device 53. When it isdetermined based on a result of the comparison that an aberration ispresent, the reflecting surface of the reflecting mirror 105 in thereflection varying unit 100 is adjusted by being deformed by operatingthe actuators 110 disposed on the back side of the reflecting surface.Then, the amount of the wavefront aberration is measured again. Thisprocess of adjusting the reflecting surface of the mirror 105 andmeasuring the aberration is repeated until an amount of the aberrationlowers down below a predetermined threshold. The reflecting mirror 105is disposed at a position of an exit pupil of the objective lens 21, forinstance.

There will be now described an example of a method of adjusting thelenses of the detection optical system 20, by referring to FIGS. 6 to13. FIG. 6 is a schematic diagram of an interferometer apparatus 360that can adjust a lens aberration of the detection optical system 20 bymeasuring interference fringes for each of the objective lens 21 and theimage forming lens 23.

That is, in the interferometer apparatus 360 shown in FIG. 6, a laserbeam L0 emitted from a laser light source 300 is first enlarged to asize by a beam expander optical system 305, and then split by a halfmirror 310 into a transmitted component and a reflected component. Thecomponent transmitted through the half mirror 310 is reflected by thereflection varying unit 100 (or the mirror 340) to be incident on aplane mirror 325 (or a spherical mirror 320). On the other hand, thecomponent of the light reflected by the half mirror 310 enters areference mirror 330. The reflection varying unit 100 and the mirror 340are retractable from an optical path, and the plane mirror 325 and thespherical mirror 320 are retractable from an optical path, by respectivemechanisms not shown. The two light beams respectively reflected by theplane mirror 325 and the reference mirror 330 return to the half mirror310 along respective incoming optical paths. The light beam reflected bythe plane mirror 325 is reflected by the half mirror 310, while thelight beam reflected by the reference mirror 330 is transmitted throughthe half mirror 310, so that the two light beams overlap and enter thedetecting device 315. The reference mirror 330 is placed on a fineadjustment stage 335 that is displaced in the Z-axis direction by asmall amount based on a signal sent from the fringe analyzing apparatus350 via a controller 334. Reference numerals 351, 352 and 353respectively denote an input/output device, a display device, and astorage device.

Referring to a flowchart of FIG. 9, there will be described an exampleof a procedure of adjusting a rear lens group system 19 including theimage forming lens 23 of the detection optical system 20, by using theinterferometer apparatus 360.

Initially, as shown in FIG. 6, the reflection varying unit 100 isswitched or replaced with the mirror 340 so that the mirror 340 is setin the optical path, and the plane mirror 325 is switched or replacedwith the spherical mirror 320 so that the spherical mirror 320 is set inthe optical path.

Then, with the beam expander optical system 305 retracted from theoptical path, a laser beam emitted from the laser light source 300 issplit by the half mirror 310 into two components that enter andreflected by the spherical mirror 320 and the reference mirror 330,respectively, and return along the incoming paths, to be reflected by ortransmitted through the half mirror 310 and then synthesized. Thesynthesized beam is incident on detecting device 315. That the twocomponents of the laser beam meet on the detecting device 315 isconfirmed (S1200).

Then, as shown in FIG. 7, the beam expander optical system 305 is set inthe optical path, and the rear lens group system 19 as an adjustablelens constructed such that the movable lenses 401-403 are incorporatedin a lens barrel, is set such that an image forming position is locatedon the side of the spherical mirror 320 (S1250). The interval betweenthe movable lenses 401-403 is set at an initial value.

Then, with the fringe analyzing apparatus 350, the wavefront aberrationis measured (S1260). The adjustable lens 19 is adjusted based on themeasured aberration, so that the shape of the interference fringeschanges from that of FIG. 8A to that of the FIG. 8B on a monitor screenof the display device 352 (S1270). The aberration is again measured withthe fringe analyzing apparatus 350, and it is determined whether theamount of the aberration is not larger than the predetermined threshold(S1280). When the amount of the aberration is larger than the threshold,the steps S1260-S1280 are repeated.

There will be described an example of a procedure of adjusting a frontlens group system 18 of the detection optical system 20 which includesthe objective lens 21 and the reflection varying unit 100, with theinterferometer apparatus 360, by referring to a flowchart of FIG. 11.

Initially, in the interferometer apparatus 360 shown in FIG. 6, thereflection varying unit 100 is switched or replaced with the mirror 340so that the mirror 340 is set in the optical path, and the referencemirror 330 is roughly adjusted so that the interference fringes 301shown in FIG. 8A appear on a screen of the display device 352, and thenmore finely adjusted to make the interference fringes 301 appear likeinterference fringes 302 as shown in FIG. 8B. In this way, theinterferometer apparatus 360 is calibrated (S1300).

Then, the reflection varying unit 100 is switched or replaced with themirror 340 (S1310). A flatness of the reflecting mirror 105 of thereflection varying unit 100 is measured with the fringe analyzingapparatus 350, and the amount of the wavefront aberration is calculated(S1320). Based on the obtained amount of the wavefront aberration, acorrection value is calculated, and the reflecting mirror 105 of thereflection varying unit 100 is deformed by driving the actuators 110 soas to adjust the amount of the aberration (S1330).

After the adjustment, the interference fringes are again observed on themonitor of the display device 352 and the aberration amount iscalculated with the fringe analyzing apparatus 350. It is determinedwhether the aberration amount is not larger than the predeterminedthreshold (S1340). When the aberration amount is larger than thepredetermined threshold, steps S1320-1340 are repeated.

Next, as shown in FIG. 10, the front lens group system 18 is set in thedetection optical system (S1350), and the wavefront aberration ismeasured with the fringe analyzing apparatus 350 (S1360). The front lensgroup system 18 as an adjustable lens is adjusted based on themeasurement of the aberration, so that the shape of the interferencefringes on the monitor screen of the display device 352 is changed fromthat of FIG. 8A to that of FIG. 8B (S1370) The measurement of theaberration with the fringe analyzing apparatus 350 is again made, and itis determined whether the aberration amount is not larger than thepredetermined threshold (S1380). When the aberration amount is largerthan the threshold, the steps S1360-S1380 are repeated.

The front lens group system 18 as has been adjusted according to theabove-described steps, is combined with the rear lens group system 19,and then an overall adjustment of the detection optical system 20 isimplemented. Hereinafter, there will be described how to adjust thedetection optical system 20 as a whole, by referring to FIG. 12.

The laser beam L0 emitted from the laser light source 300 is enlarged bya beam expander optical system 311, and bent by a mirror (not shown) tothe Y-axis direction, and then reflected in the Z-axis direction by themirror 307 to enter the condenser lens 308. Thereafter, the laser beamL0 forms a laser spot at a position of a front focus of the objectivelens 21, namely, at a surface to be inspected. The laser spot enters theobjective lens 21 and forms a spot image at the image forming positionof the detection optical system 20, and thus enters the detecting device315 disposed at the image forming position. The detecting device 315outputs an image signal to the fringe analyzing apparatus 350.

The fringe analyzing apparatus 350 measures an aberration of the spotimage based on the image signal from the detecting device 315, and arelative position between the front lens group system 18 and the rearlens group system 19 is adjusted so as to minimize the aberration. Themeasurement of the aberration and the positional adjustment of the lenssystem are repeated until the aberration amount lowers below thepredetermined threshold. A result of the adjustment is stored in astorage device 353, as data associated with that detection opticalsystem 20, and used as reference data after installation of thedetection optical system 20 in the defect inspecting apparatus.

The thus adjusted detection optical system 20 is installed in the defectinspecting apparatus as shown in FIG. 14, and the image formationperformance of the detection optical system 20 can be maintained at thelevel at the time of the production, by the wavefront measuring opticalsystem 150.

The number of lenses of the objective lens 21 and that of the imageforming lens 23 as components of the detection optical system 20 areexpected to increase. An a spherical lens may be used to reduce thenumber of the lenses significantly. This can be effective to reduce theweight of the detection optical system 20, and the number of assemblysteps thereof.

A foreign particle/defect inspection is required for a multilayer wafer,too, on a surface of which a transparent film (e.g., an oxide film) isformed. That is, a multilayer wafer is produced by repeating a step offorming a pattern on a transparent film. In an inspection of foreignparticle on a wafer with an oxide film thereon, there are increasingneeds for detecting only foreign particles on a surface of the oxidefilm. Basically, it is possible to inhibit reflecting light from asubstrate, e.g., light diffracted by a pattern, from affecting theinspection, by having the illumination angle α small. However, by makingthe illumination angle α small, a part of the scattered light from aforeign particle on the side of the regular reflection with respect tothe illumination beam, i.e., forward scattering light, increases, whileentrance of the scattered light into the detection optical systemdisposed above decreases, thereby making a stable detection of foreignparticle impossible.

Hence, the invention uses the apparatus shown in FIG. 14 to detectforeign particles. Although the illumination optical system 10 has thesame structure as shown in FIG. 2B, the optical elements disposed alongthe optical path L2 starting from the splitting optical element 218, andreference numerals of some parts corresponding to those in FIG. 2B, areomitted in FIG. 14. In the system shown in FIG. 14, a laser beam emittedfrom the light source 11 is enlarged in its diameter by the beamexpander optical system 16, and reflected by the splitting opticalelement 218 in the direction of the optical path L3, to irradiate thewafer 1 with the slit-like beam 201 from an illumination angle γ fromthe illumination direction 250, via the mirror 251, the beam diametercorrection optical system 252, the mirrors 253, 254, 256, and thecylindrical lens 255. A detection optical system including an imageforming lens 630 and a detecting device 640 is disposed in a direction260 that intersects the illumination direction 250 and forms a detectionangle δ (i.e., an inclination angle with respect to the surface of thewafer 1), thereby enabling to detect side scarred light from the foreignparticle on the surface of the thin film on the wafer, by irradiatingthe wafer 1 with the slit-like beam 201 from the illumination direction250. A light receiving surface of the detecting device 640 and a surfacearea irradiated with the slit-like beam 201 are in a positionalrelationship to enable formation of an image, and the image formationmagnification of the image forming lens 630 is set such that the lightreceiving surface of the detecting device can encompass an entireilluminating range of the slit-like beam 201.

By having the detection system in the positional relationship to form animage, an influence of stray light from an object other than the objectto be inspected is prevented, while the speed of the inspection isincreased since parallel processing is possible. During the inspection,the light receiving surface of the detecting device is controlled by anautofocus control system (not shown) so as to encompass the entireilluminating range of the slit-like beam 201 in order that the surfaceof the wafer is at a predetermined position in the Z-axis direction. Asthe detecting device 640, a TDI image sensor is employed, for instance,similarly to the detecting device 26. It is possible to dispose aspatial filter having the same function as the spatial filter 22described with respect to FIG. 1, in the optical path, in order to blockreflected diffracted light from the pattern. The illumination may bemade from the direction 220 or 230 shown in FIGS. 2B and 2C. However, itis desirable that the illuminating means and the detection opticalsystem including the image forming lens 630 and the detecting device 640are disposed so as not to interfere, and the illumination and detectionsystems are disposed in directions and at angles that can prevent aninfluence of the reflected light from the substrate such as diffractedlight from the pattern, namely, at optimum positions empiricallyobtained.

There will be described the signal processing system 40 which processessignals outputted from the light detecting device 26 that receives thereflected diffracted light from the wafer 1 and implements photoelectricconversion, by referring to FIG. 15. The system shown in FIG. 15 is anexample where a single signal processing circuit is provided in thesignal processing system 40. However, where the detecting device 26 hasa plurality of output channels, it is necessary to provide, in thesignal processing system 40, a plurality of circuits each having thesame structure as the signal processing system of the presentembodiment.

The signal processing system 40 includes: an A/D converter 1301; a datastoring portion 1302 that stores a detected image signal f(i, j) asA/D-converted; a threshold calculating and processing portion 1303 thatimplements a threshold calculation based on the detected image signal;foreign particle detecting and processing portions 1304 a-1304 n each ofwhich includes a plurality of circuits for implementing foreign particledetection processing for respective merge units, based on the detectedimage signal 1410 obtained from the data storing portion 1302, and athreshold image signal 1420 (Th(H), Th(Hm), Th(Lm), Th(L)) obtained fromthe threshold calculating and processing portion 1303; a characteristicquantity calculating circuit 1310 which calculates characteristicquantities such as an amount of scattered light from defect obtained bya detection with a low angle illumination, an amount of scattered lightfrom defect obtained by a detection with a high angle illumination, andthe number of detection pixels indicating a range of the defect; aninspection result integrating and processing portion 1309 thatcategorizes the defects such as minute/large foreign particles, patterndefect, and microscratch on the semiconductor wafer, based on thecharacteristic quantities of the respective merge units obtained fromthe characteristic quantity calculating circuit 1310; and a resultdisplay portion 1311.

Each of the foreign particle detecting and processing portions 1304a-1304 n includes a pixel merge circuit 1305 a-1305 n, 1306 a-1306 n, aforeign particle detecting and processing circuit 1307 a-1307 n, and aninspection area processing portion 1308 a-1308 n, correspondingly tomerge operators of 1×1, 3×3, 5×5 . . . and n×n, respectively.

The signal obtained by the light detecting device 26 is digitized by theA/D converter 1301, and the detected image signal f(i, j) 1410 is storedin the data storing portion 1302, as well as sent to the thresholdcalculating and processing portion 1303. The threshold calculating andprocessing portion 1303 calculates the threshold image signal Th(i, j)1420 for foreign particle detection, and the foreign particle detectingand processing circuit 1307 of each merge operator detects foreignmaterial, based on the signal processed by the pixel merge circuits1305, 1306.

The inspection area processing portion 1308 processes the signal ofdetected foreign material and the threshold image signal depending onthe place of the detection. At the same time, based on the signalsobtained from the pixel merge circuits 1305 a-1305 n, 1306 a-1306 n, theforeign particle detecting and processing circuits 1307 a-1307 n, theinspection are a processing portions 1308 a-1308 n, that are included inthe foreign particle detecting and processing portions 1304 a-304 n ofthe respective merge operators, the characteristic quantity calculatingcircuit 1310 calculates the characteristic quantities (e.g., an amountof the scattered light obtained with high angle illumination, an amountof scattered light obtained with low angle illumination, the number ofdetection pixels with defect), and the inspection result integrating andprocessing portion 1309 integrates the foreign particle signal with thecharacteristic quantities, and a result of the inspection is presentedon a result display portion 1311.

More specifically, initially, the A/D converter 1301 is a circuit havinga function to convert an analog signal obtained by the light detectingdevice 26 into a digital signal, and the number of bits of theconversion is desirably 8 bits to 12 bits, since when the bit number istoo small, the resolution of the signal processing lowers, makingdetection of minute light difficult, while when the bit number is toolarge, the A/D converter is expensive, increasing the cost of theapparatus. The data storing portion 1302 is a circuit for storing thedigital signal.

Then, by referring to FIG. 16, the pixel merge circuits 1305, 1306 willbe described. The pixel merge circuits 1305 a-1305 n, and 1306 a-1306 n,are constituted by different merge operators 1504.

The merge operators 1504 function to integrate, in a range of n×npixels, the detected image signal f(i, j) 1410 obtained from the datastoring portion 1302, and the difference threshold image signal 1420constituted by a detection threshold image signal Th(H), a detectionthreshold image signal Th(L), a verification threshold image signalTh(Hm), and a verification threshold image signal Th(Lm), and obtainedfrom the threshold calculating and processing portion 1303. Forinstance, the merge operator is a circuit that outputs a mean value ofn×n pixels.

For example, the pixel merge circuits 1305 a, 1306 a is constituted by amerge operation for merging of 1×1 pixel, the pixel merge circuits 1305b, 1306 b is constituted by a merge operator for merging 3×3 pixels, thepixel merge circuits 1305 c, 1306 c is constituted by a merge operatorfor merging 5×5 pixels, . . . and the pixel merge circuits 1305 n, 1306n is constituted by a merge operator for merging n×n pixels. The mergeoperator for merging of 1×1 pixel outputs the input signals 1410, 1420without any processing.

As described above, the threshold image signal is constituted by fourimage signals (Th(H), Th(Hm), Th(Lm), Th(L)), each of the pixel mergecircuit portions 1306 a-1306 n requires four merge operators Op. Hence,each of the pixel merge circuits 1305 a-1305 n outputs merged detectedimage signals 431 a-431 n that are the detected image signal asprocessed or merged by the merge operators 1504. Meanwhile, the pixelmerge circuit portions 1306 a-1306 n outputs merged threshold imagesignals 441 a (441 a 1-441 a 4)-441 n (441 n 1-441 n 4) that are thefour threshold image signals (Th(H), Th(Hm), Th(Lm), Th(L)) as merged bymerge operators Op1-Opn. The merge operators in the pixel merge circuitportions 1306 a-1306 n are the same.

The effect of merging of the pixels will be illustrated. In a foreignparticle inspection, not only a minute foreign particle but also a largethin-film shaped foreign particle that spreads in a range of severalmicrometers should be detected without oversight. However, the detectedimage signal from such a thin-film shaped foreign particle is notnecessarily strong, the S/N ratio of the pixel-by-pixel detected imagesignal is low, which may cause an oversight. Thus, the unit of thedetection is n×n pixels corresponding to the size of the thin-filmshaped foreign particle and a convolution calculation is implemented, inorder to improve the S/N ratio.

There will be now described the inspection area processing portions 1308a-1308 n. The inspection area processing portions 1308 a-1308 n operateto process the foreign particle/defect detection signals obtained fromthe foreign particle detecting and processing circuits 1307 a-1307 nwith an identification of the chip in question, namely, to delete dataof an area (including one inside a chip) not requiring the inspection,to vary the detection sensitivity for each area (including one inside achip), and to select an area desired to inspect.

The inspection area processing portions 1308 a-1308 n may operate suchthat when an area on the object substrate 1 does not require a highdetection sensitivity, a threshold obtained by a threshold calculatingportion 1411 of the threshold calculating and processing portion 1303 isset at a high level at that area, or such that data on a foreignparticle only in an area desired to be inspected is maintained based oncoordinates of the foreign particle and from data of the foreignparticle outputted from the foreign particle detecting and processingcircuits 1307 a-1307 n.

The area where the detection sensitivity is not required to be high is,for instance, an area where the density of the circuit pattern on theobject substrate 1 is low. Reducing the detection sensitivityefficiently reduces the number of detected foreign particles/defects.That is, a defect inspecting apparatus with high sensitivity may detectseveral tens of thousands of foreign particles, in some situations.However, the thing really matters is foreign particles in an area wherethe circuit pattern is present, and it is a shortcut to take measuresagainst the significant foreign particles in improving the yield rate inthe device production.

However, when the entire area on the object substrate 1 is inspectedwith a same degree of sensitivity, the significant and non-significantforeign particles are mixed, thereby making it difficult to extract thesignificant foreign particles. Hence, the inspection area processingportions 1308 a-1308 n lower the detection sensitivity for the areawhere the circuit pattern is not present and thus which does not muchaffect the yield rate, based on CAD information or threshold mapinformation in the chip, so as to efficiently extract the significantforeign particles. However, the way of extracting the significantforeign particles is not limited to the method of varying the detectionsensitivity, but may be otherwise. For instance, the significant foreignparticles may be extracted by categorizing the foreign particles, asdescribed later, or based on the size of the foreign particles.

There will be described the inspection result integrating and processingportion 1309 and its inspection the result display portion 1311. Theinspection result integrating and processing portion 1309 integrates theresults of the foreign particles that are processed in parallel by thepixel merge circuits 1305, 1306, integrates the characteristicquantities calculated by the characteristic quantity calculating circuit1310 and the results of the foreign particle detection, and send theintegrated result to the result display portion 1311. This inspectionresult integration processing is desirably implemented by a PC or othersso as to facilitate a change in the content of the processing.

First, there will be described the characteristic quantity calculatingcircuit 1310. The characteristic quantities represent thecharacteristics of the detected foreign particle and the defect, and thecharacteristic quantity calculating circuit 1310 is a processing circuitwhich calculates the characteristic quantities, that may be, forinstance, an amount of the reflected diffracted light (i.e., an amountof the scattered light) (Dh, Dl) from a foreign material or a defectwith high angle and low angle illumination, the number of detectionpixels, the shape of the area where the detection of foreign particle isimplemented, and the direction of a principal axis of inertia, thedetected place on the wafer, the kind of the circuit pattern of thesubstrate, a threshold value used when detecting foreign particle.

[Employment of a microscope] The defect inspecting apparatus of theembodiment includes the observation optical system 60 with which theforeign particle detected by the inspection is confirmable, as shown inFIG. 17. By moving the stages 31, 32, the detected foreign particle onthe wafer 1 (including false information) is moved into a field of viewof a microscope of the observation optical system 60, and an image ofthe microscope is observed.

An advantage of including the observation optical system 60 is that thedetected foreign particles is immediately observable, without moving thewafer to a review device such as SEM. By instantaneously observing theforeign particle detected by the defect inspecting apparatus, a causalof the foreign particle is quickly identified. An image of the foreignparticle taken by the TV camera 64 of the observation optical system 60is displayed on a color monitor commonly used for a personal computer,and thus an inspection around the coordinates of the detected foreignparticle by a local irradiation with a laser beam and stage scanning ispossible, and also there is a function to display an image of scatteredlight from the foreign particle and a marked position of the foreignparticle, on the monitor. Thus, it is possible to confirm whether aforeign particle is actually detected or not. The local image taken bystage scanning enables comparison or confirmation at the moment since animage of a die next to the die in which a foreign particle is detectedcan be taken.

A light source of the observation optical system 60 may be visible light(e.g., white light). Alternatively, the observation optical system 60may be a microscope whose light source is ultraviolet light. To observea particularly minute foreign particle, a microscope with highresolution, e.g., a microscope using ultraviolet light is desirable.When a microscope using visible light is employed, color information onthe foreign particle is obtained, thereby facilitating recognition ofthe foreign particle.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

1. An apparatus for inspecting a foreign particle defect, comprising: anilluminator which irradiates a surface of a sample with an illuminatingbeam; a detector which collects through an objective lens scatteredreflected light from the surface of the sample as illuminated by theilluminator and detects the collected light with a detecting device; anda signal processor which processes a signal obtained as a result of thedetection of the scattered reflected light by the detecting device ofthe detector so as to detect a foreign particle defect on the surface ofthe sample, wherein the detector includes a converging optical systemwhich collects the scattered reflected light from the surface of thesample, and an aberration corrector which corrects an aberration of theconverging optical system, wherein the illuminating beam emitted fromthe illuminator toward the surface of the sample is formed in a shapelong in a direction, and emitted from a direction oblique to the surfaceof the sample, and wherein the converging optical system of the detectorincludes a reflection optical system and a refraction optical system,and the aberration corrector corrects the aberration of the convergingoptical system by changing a reflection condition of the reflectionoptical system or a refraction condition of the refraction opticalsystem.
 2. The apparatus according to claim 1, wherein the illuminatorhas a first illuminating portion which irradiates the surface of thesample with an illuminating beam from a high angle, and a secondilluminating portion which irradiates the surface of the sample with anilluminating beam from a low angle.
 3. An for inspecting a foreignparticle defect, comprising: an illuminator which irradiates a surfaceof a sample with an illuminating beam; a detector which collects throughan objective lens scattered reflected light from the surface of thesample as illuminated by the illuminator and detects the collected lightwith a detecting device; and a signal processor which processes a signalobtained as a result of the detection of the scattered reflected lightby the detecting device of the detector so as to detect a foreignparticle defect on the surface of the sample, wherein the detectorincludes a converging optical system which collects the scatteredreflected light from the surface of the sample, and an aberrationcorrector which corrects an aberration of the converging optical system,wherein the illuminating beam emitted from the illuminator toward thesurface of the sample is formed in a shape long in a direction, andemitted from a direction oblique to the surface of the sample, andwherein the converging optical system of the detector further includesan image forming magnification changer which changes an image formingmagnification of the converging optical system while a position of theobjective lens relatively to the detecting device is fixed.
 4. Theapparatus according to claim 3, wherein the detecting device of thedetector is a time delay integration sensor which outputs detectionsignals in parallel, and the signal processor processes in parallel thesignals as outputted in parallel from the time delay integration sensor.5. A method for inspecting a foreign particle defect, comprising thesteps of: irradiating a surface of a sample with an illuminating beam;collecting, with a converging optical system, scattered reflected lightfrom the irradiated sample, and detecting at a desired magnification animage of the scattered reflected light as collected; and processing asignal obtained as a result of the detection of the scattered reflectedlight, and detecting a foreign particle defect on the surface of thesample, wherein the image of the scattered reflected light from thesurface of the sample is detected by correcting an aberration of theconverging optical system according to the desired magnification,wherein the irradiating step comprises forming the illuminating beam ina shape long in a direction, and emitting the illuminating beam from adirection oblique to the surface of the sample, and wherein theirradiating step comprises irradiating the surface of the sample with anangle from which the illuminating beam is emitted being switched betweena high angle and a low angle.
 6. The method according to claim 5,wherein the irradiating step comprises irradiating the surface of thesample with an angle from which the illuminating beam is emitted beingswitched between a high angle and a low angle.
 7. The method accordingto claim 5, wherein the detecting step comprises detecting the image ofthe scattered reflected light with a time delay integration sensor ofparallel output type, and the processing step comprises in parallelprocessing signals outputted from the time delay integration sensor inparallel.